DEMOGRAPHIC RESPONSE OF GOLDEN-WINGED WARBLER TO HABITAT MANAGEMNET ACROSS A CLIMATE CHANGE GRADIENT IN THE CORE OF THE SPECIES' RANGE: 2012 SUMMARY REPORT

Abstract

In 2012 we repeated our 2011 efforts with a substantial increase in data collected. This was the second and final full field season investigating population ecology of Golden-winged Warblers (Vermivora chrysoptera; hereafter GWWA) at Tamarac National Wildlife Refuge (NWR) and Rice Lake NWR in Minnesota and Sandilands Provincial Forest (PF) in Manitoba. We assessed nesting habitat use, nest productivity, fledgling survival, and post-fledging habitat use by GWWA at all three sites. We color banded 107 adult female and 112 adult male GWWA and we attached radio transmitters to 108 adult females. By tracking radio-marked females and by nest searching, we found and monitored 149 nesting attempts including 2 nests found by others conducting research at Tamarac NWR (see acknowledgments). The 66% increase over the 2011 nest sample was partly due to increased effort to radio-mark adult females, but mostly to the return of many experienced nest searchers from 2010 and 2011. We banded 311 nestlings and fledglings and radio-tracked 175 fledglings. We collected data on habitat characteristics and GWWA behavior at >2,400 adult, nest, and fledgling locations. Including renesting, we estimated that 58%, 74%, and 79% of females successfully nested and that 53%, 49%, and 48% of fledglings survived to independence from adult care at Tamarac NWR, Rice Lake NWR, and Sandilands PF, respectively. Interestingly, the increases (over 2011) in successfully nesting females at Rice Lake NWR and Sandilands PF were accompanied by considerable decreases in fledged brood size due to many partial-brood nest predation events, and the decrease in successfully nesting females at Tamarac NWR was accompanied by a considerable increase in fledged brood size. Similar to 2011, nest failure and fledgling mortality were due nearly entirely to predation at the Minnesota sites, whereas weather exposure and blowfly infection accounted for a relatively high percentage (23%) of fledgling mortalities at Sandilands PF. Unlike previous years, we tracked at least one (total = 6) nestling or young fledgling at each site to a garter snake (i.e., inside the snake), possibly reflective of the warmer, dryer early spring weather. Consistent with 2011, 30% of radio-marked females nested in older forest stands traditionally not considered GWWA habitat, and fledged family groups moved into and spent much of the post-fledging period in those older forest areas. Early findings from this project have been disseminated in 2 peer reviewed scientific journal articles and 2 more are currently in review. Detailed analyses for manuscripts about transmitter effects, population dynamics, micro- and macro-scale habitat associations, nest-site choice, parental care of fledglings, and interesting natural history observations are all underway.